The invention relates to front lift equipment for a crawler tractor, for agricultural use, which tractor has a substantial overhang of its front part relative to an intermediate transverse girder to which there is fixed, on each side, a crawler set, generally adjustable transversely to adjust the track of the tractor, there being an axle at the rear of the tractor, the equipment comprising a reinforcing member arranged on each side of the tractor, continuing forward beyond the intermediate girder, and means of connection between the front part of the reinforcing member and a point of attachment of a part subjected to the forces generated by a load acting on the front lift.
Current generations of crawler tractors for agricultural use have three main characteristics compared to the conventional versions of these tractors:
rubber crawler tracks;
a lower weight per kilowatt of power in order to avoid compacting the ground excessively;
a substantial overhang of the front part of the tractor so that the tractor is balanced in spite of the nose-up moment created by an implement trailed behind the tractor, so as to ensure uniform contact of the crawlers to encourage the transmission of power and avoid compacting the ground.
The intermediate girder constitutes the furthest forward bearing element of the framework of the crawler tractor. This intermediate girder is practically mid-way along the length of the tractor. When a load is carried at the front of the tractor, a considerable bending moment is produced on that part of the tractor located forward of the intermediate girder. It is therefore necessary to be able to control this bending moment to avoid causing mechanical failure of the tractor.
A front lift is not installed as a matter of course on all crawler tractors. In order to avoid extra cost for the users of tractors not equipped with front lifts, and with a view to limiting the total weight of the tractor, tractor manufacturers do not organize the framework of the tractor according to the loadings created by any front lift that might be fitted.
It is therefore important that the manufacturers of front lifts, installed later, provide a structure for reinforcing the crawler tractor to prevent it from being subjected to unacceptable loadings. A reinforcing member arranged on each side of the tractor forms part of this reinforcing structure.
Such a reinforcing member leads to drawbacks, particular the following ones.
The crawler sets are adjustable, in the transverse direction, to make it possible to modify the track of the tractor. This adjustment is obtained by shifting the zone of attachment of the set along the intermediate girder. The presence of a reinforcing member located between the crawlers and the body of the tractor leads to a limitation on the amount of adjustment of the track of the tractor, particularly when the issue is one of setting this track to the minimum value.
Furthermore, the presence of a reinforcing member at the bottom of the tractor encourages the build-up of waste under the tractor.
The object of the invention is, above all, to provide a front lift equipment for a crawler tractor that makes it possible to avoid the abovementioned drawbacks while at the same time remaining relatively simple and economical in its structure and use, and at the same time providing the tractor with sufficient reinforcement.
According to the invention, a front lift equipment for a crawler tractor for agricultural use, of the above-defined kind, is characterized in that each reinforcing member has a flank of small thickness, roughly parallel to the vertical mid-plane of the tractor, located in the vicinity of the body of the tractor, the height of the flank being designed to provide satisfactory mechanical strength, the thickness of the flank being such that the setting of a narrow tractor crawler track is not impeded.
Advantageously the flank has a thickness not exceeding 50mm, particularly not exceeding 30mm.
The flank passes over and bears on the intermediate girder and is continued rearward to be connected to the rear axle.
The flank may be formed of two parts assembled by a joint, particularly an inclined joint. The joint is preferably located roughly at the level of the intermediate girder and the part of the flank located forward of the joint is thicker than the part of the flank located to the rear of the joint.
The front lift may comprise a supporting structure, particularly in the shape of an inverted U, carrying the three hitching points for an implement, this supporting structure being articulated, on each side, at the bottom rear part, to one end of a longeron which is articulated at its other end to a pivot carried by the framework of the tractor, the supporting structure being held on each side by a tensioning means, particularly a tensioning screw, provided between a high point on the supporting structure and a point secured to the longeron, the connecting means (L) being formed of rams allowing the raising or lowering of the longerons, and the supporting structure.
The tensioning screws may be equipped with a sliding part to allow longitudinal following of the relief.
According to another possibility, the equipment comprises a lift fixed to the front of the tractor, with rams and articulated arms, the articulation of the arms being located at the front of the tractor, and the connecting means are provided between the front top end of the flank and a point of attachment located further forward and lower down, secured to the framework of the tractor, particularly located on a part attached and fixed to the tractor and serving to attach the lift.
The connecting means advantageously converge from the rear forward.
There may be provided, on each side of the tractor, a link rod articulated, particularly on a ball joint, at each end to establish a transverse connection between the top front end of the flank and a point on the framework of the tractor so as to combat the transverse loadings that act on the front end of the flank.
Each connecting means may consist of a rigid bar, particularly a preloaded one.
According to an advantageous solution, the connecting means consist, on each side, of a ram supplied in parallel with the front lift rams.
A pressure sensor and a nonreturn valve controlled by the pressure sensor are advantageously located on the supply line of the rams forming connecting means so as to cut the communication between these rams and the lift rams when a given pressure value is exceeded.
The invention also relates to a crawler tractor equipped with front lift equipment as defined hereinabove.